Romaria mine, Romaria, Bagagem River valley, Coromandel, Minas Gerais, Brazili

Regional Level Types
Romaria mine	Mine
Romaria	- not defined -
Bagagem River valley	Valley
Coromandel	- not defined -
Minas Gerais	State
Brazil	Country

This diamond mine was opened around 1867 following the discovery of diamonds in the nearby Água Suja stream, a tributary of the Bagagem river. The mine closed in 1984. While most diamonds in the Coromandel district were obtained from alluvial deposits, at Romaria diamonds were mined from a lithified conglomerate in the river bottomland. This conglomerate has been interpreted as a debris flow deposit consisting of materials reworked from surrounding metasedimentary bedrock including the Neoproterozoic Araxá Group and Cretaceous sedimentary rocks (Suguio et al., 1979; Andrade and Chaves, 2009). As the debris flow apparently followed modern topographic contours, it is most likely of Quaternary age. Fleischer (1998), however, presented evidence that normal block faulting led to erosion of the original diamondiferous conglomerate on the upthrown (west) side of the faults, with deposition occurring in alluvial fans on the down-dropped side. He correlated localized outcrops of this material for a little over 40 km in an NW-SE direction and suggested the existence of a faulted lineament along nearly the entire length of the Bagagem River valley. The diamonds were probably reworked from the Mata da Corda Group of Late Cretaceous age, a resistant unit that caps the mesas on either side of the Bagagem River valley.

Lithic clasts in the conglomerate are up to 0.8 meters in size and include schist, phyllite, quartzite, basalt, reworked conglomerate, vein quartz, and siliceous concretions rich in opal. The matrix is arenaceous and contains considerable kaolinite and illite. Framework grains include mm-scale grains of heavy minerals including pyrope, staurolite, "hornblende," epidote, kyanite, monazite, tourmaline, zircon, and anatase. The opaques include magnetite, hematite, goethite, and ilmenite. The pyrope is chromium-rich, with chromium/calcium oxide ratios plotting mostly in the G4, G5, and G9 fields, indicating the poor likelihood of associated diamonds (Grütter et al., 2004). Nevertheless, diamonds from the area are large and clear, although commonly abraded and fractured, and suggest a proximal source, however, that has yet to be identified.

Modified by NK, January 2017.

Other Regions, Features and Areas containing this locality

References